1. Field of the Invention
The present invention relates to a device for applying a liquid medium to a moving product web, particularly a board web.
2. Description of the Related Art
An applicator device has been described in DE 10032500.9. In the case of this device, which is used to apply a liquid medium to one or both sides of a moving product web, especially a board web, the web runs over a roll or runs through a nip between two rolls.
At least one feed apparatus for the application medium is provided. Under operating conditions, a liquid pond then forms between the rolls or between one roll and the web. In this area of the pond, the application medium, in particular size or starch, penetrates into the product web, that is to say penetrates into the web. Specific properties of the web are intended to be changed and improved thereby.
By way of specifically shaped nozzle lips, which can be fitted to the nozzle element of the feed apparatus, the desired size of the free surface of the pond and also the immersion depth or the level can be adjusted. In order to feed the pond on one or on both sides of the web, use is made in each case of a feed apparatus having the aforementioned nozzle element and the nozzle lips. In this case, the nozzle lips form the discharge opening for the application medium.
In the case of the aforementioned solution, the nozzle lips, including the discharge opening, project into the pocket existing between material web and roll. The application medium flows approximately parallel to the running direction of the web and the roll or rolls. Nevertheless, the flow behavior of the application medium in the pond is not yet optimal. At higher required running speeds of the size press, increased and undesired eddy formation is conceivable.
The present invention provides an applicator device with which the running properties and the application options of size presses can be improved further and with which adequate penetration of the application medium into the product web, particularly into a board web, is also possible.
The invention comprises, in one form thereof, an application device for applying an application medium to at least one side of a moving product web, the web having a running direction. The application device includes at least one roll supporting the web, at least one pocket between at least one roll and at least one side, at least one pocket having a size and a shape, at least one feed apparatus including a metering element, the metering element having at least one discharge nozzle projecting into at least one pocket and at least one application chamber designed into the metering element, at least one discharge nozzle discharging the application medium onto the web in a first direction and proximate to at least one application chamber, the first direction approximately orthogonal to the running direction.
The applicator device according to the present invention is particularly suitable for the treatment of a board web.
The provision of an application chamber that projects into the pocket between roll and moving product web and from which the application medium strikes the web in an approximately orthogonal direction, that is to say transversely with respect to the running direction of the web, has a plurality of advantages. Some of the advantages of the present invention as compared with the solution cited in the description of the related art are:
1. Improvement of the flow conditions in pond operation.
2. The introduction of the application medium can be carried out with a precisely defined quantity and an appropriately defined pressure.
3. Less mist formation and less spray.
4. Reduction of the quantity of application medium etc. to be provided.
In this connection, it is very advantageous to arrange the application chamber, in which a medium pressure is built up, to be very close, that is to say at only the minimum distance from the product web to which the application medium is to be applied. As a result, there is the possibility of reducing the compressive penetration in the roll nip, as a result of which the product web is stressed less.
The applicator device according to the present invention can be operated both with normal pond operation and with a low pond level in the pocket.
One advantage of the present invention is the application possibilities for an extremely wide range of paper grades, running properties and application medium types are increased by a multiple.
With the applicator device according to the present invention, it is also possible to set only a low nip load, as a result of which, for example, the volume of a board web is preserved. The fact that only a low nip load (compressive force) is needed between board web and the roll or in the nip between two rolls implies that the rolls do not have to be highly dimensioned, which results in considerable savings in material and costs for the applicator device.
A further advantageous achievement of the present invention is that the nozzle element, that is to say the application chamber, can be equipped with discharge nozzles, which can be in the form of spray nozzles.
The spray nozzles, which can be arranged within the pressure application chamber in one or more planes, firstly ensure particularly gentle application. As a result, optimum surface consolidation of the fibers of board, when starch is used, and also keeping it free from dust is made possible, especially when processing board.
Secondly, the same applicator device permits use even in the case of graphic papers to which pigment-containing coating color is to be applied. In this case, a pond level is generally dispensed with and, in addition, the operating speeds are in this case generally significantly higher. Even a 1:1 application would be possible in this case without subsequent equalization of the applied coating color.
However, the applicator device according to the present invention is also further suitable for xe2x80x9cnormalxe2x80x9d pond operation. Such an operation is advantageous when fluting medium or liner is to be treated with starch or size and, for this purpose, a higher penetration than in the case of board is required.
In the case of board, on the other hand, a lower penetration is adequate, since as a rule the intention here is only to bond the raw material particles at the surface of the web.